Shaped and fired articles of tio2

Abstract

Solid, shaped and fired refractory articles, such as fibers and microspheres, of titanium dioxide are made by shaping, gelling, and firing titania sols. Said fibers can be made by extruding in air a viscous aqueous titania sol, and heating and firing the resulting green fiber to remove water, decompose and volatilize undesired constituents, and form a refractory fiber of polycrystalline titanium dioxide, which is useful, for example, to form refractory fabrics or as reinforcement for composites. Said microspheres can be made by dispersing droplets of an aqueous titania sol in an organic dehydrating liquid, separating the resulting green microspheres from the dehydrating liquid, and heating and firing the green microspheres to form solid refractory microspheres of polycrystalline titanium dioxide, which are useful, for example, in reflective signs or traffic marking surfaces. Said fired fibers and microspheres are preferably transparent to visible light with the titanium dioxide content thereof in its anatase form.

What is claimed is: 
     
       1. A transparent, solid, shaped and fired, non-vitreous, homogeneous, continuous refractory fiber comprising predominantly polycrystalline titanium dioxide in its anatase form. 
     
     
       2. Transparent, solid, shaped and fired, non-vitreous, homogeneous microspheres having diameters in the range of 1 to 200 microns and comprising predominantly polycrystalline titanium dioxide in its anatase form. 
     
     
       3. The microspheres of claim 2 further comprising one or more of other metal oxide. 
     
     
       4. A plastic, elastomeric, metallic or ceramic composite with a plurality of microspheres of claim 2 distributed therein. 
     
     
       5. A solid, shaped and fired, non-vitreous, homogeneous, transparent, continuous refractory fiber comprising predominantly polycrystalline titanium dioxide in its anatase form, and one or more other metal oxides. 
     
     
       6. The fiber of claim 5, wherein said other metal oxide is chromium oxide. 
     
     
       7. The fiber of claim 5, wherein said other metal oxide is alumium oxide. 
     
     
       8. The fiber of claim 5, wherein said other metal oxide is iron oxide. 
     
     
       9. The fiber of claim 5, wherein said other metal oxide is cobalt oxide. 
     
     
       10. The fiber of claim 5, wherein said other metal oxide is silica. 
     
     
       11. The fiber of claim 5, wherein said other metal oxide is chromium oxide and silica. 
     
     
       12. A solid, shaped and fired, non-vitreous, homogeneous, transparent, continuous, refractory fiber comprising predominantly polycrystalline titanium dioxide in its anatase form, and one or more other metal oxides selected from the group consisting of chromium oxide, aluminum oxide, iron oxide, cobalt oxide, and silica. 
     
     
       13. A solid, shaped and fired, non-vitreous, homogeneous, transparent, continuous, refractory fiber comprising predominantly polycrystalline titanium dioxide in its anatase form, and one or more other metal oxides present in an amount sufficient to impart a color to said fiber. 
     
     
       14. Transparent, solid, shaped and fired, non-vitreous, homogeneous microspheres comprising predominantly polycrystalline titanium dioxide in its anatase form and one or more of the oxides of silicon, chromium, aluminum, iron, and cobalt. 
     
     
       15. A method for forming continuous fibers of solid, transparent refractory comprising predominantly polycrystalline titanium dioxide in its anatase form, which method comprises extruding in air an aqueous acidic titanium oxide sol or aqueous acidic mixture of a titanium compound calcinable in air to titanium dioxide, and heating and firing the resulting amorphous fibers to remove water, acid, organic material, and carbon therefrom and form said continuous fibers. 
     
     
       16. A method according to claim 15 wherein the material which is extruded to form said amorphous fibers is a viscous, fiberizable concentrate comprising an aqueous titanium dioxide sol prepared by dispersing in water a gel formed by drying an acidified aqueous mixture of tetraalkyl titanate. 
     
     
       17. A method according to claim 16 wherein said firing is carried out at a temperature up to about 600° C. 
     
     
       18. A method according to claim 15 wherein the material which is dispersed as said droplets to form said amorphous microspheres comprises an aqueous titanium dioxide sol prepared by dispersing in water a gel formed by drying an acidified aqueous mixture of tetraalkyl titanate. 
     
     
       19. The method according to claim 18 wherein said tetraalkyl titanate is tetraisopropyl titanate. 
     
     
       20. The method of claim 16 wherein said tetraalkyl titanate is tetraisopropyl titanate. 
     
     
       21. The method of claim 16, wherein said aqueous mixture of said tetraalkyl titanate further comprises a further metal oxide or metal compound which is calcinable in air to its corresponding metal oxide and the resulting shaped and fired refractory article further comprises said metal oxide. 
     
     
       22. The method of claim 21 wherein said metal oxide is silica. 
     
     
       23. The method of claim 21 wherein said metal oxide is alumina. 
     
     
       24. The method of claim 21 wherein said metal oxide is chromia. 
     
     
       25. The method of claim 21 wherein said metal oxide is chromia and silica. 
     
     
       26. A method for forming refractory microspheres of solid transparent refractory comprising predominantly polycrystalline titanium dioxide in its anatase form, which method comprises dispersing as droplets in an organic dehydrating liquid an aqueous acidic titanium oxide sol or aqueous acidic mixture of a titanium compound calcinable in air to titanium dioxide, recovering the resulting amorphous microspheres from said liquid, and heating and firing said recovered microspheres to convert them to said refractory microspheres. 
     
     
       27. In a retro-reflective sheeting comprising a monolayer of spherical lense elements and associated reflector adapted in combination therewith to provide retro-reflection, the improvement comprising using as said lense elements transparent, solid, shaped and fired microspheres comprising predominantly polycrystalline titanium dioxide in its anatase form. 
     
     
       28. A plastic composite comprising a plastic matrix having dispersed therein a plurality of solid, shaped and fired, non-vitreous, homogeneous, refractory fibers comprising predominantly polycrystalline titanium dioxide in its anatase form.